1. Field of the Invention
The claimed invention relates generally to web transport apparatus, and more particularly to the structure of a honeycomb machine in which web material is fed incrementally to a cyclic cutter through a resiliently stabilized web movement.
2. Description of the Prior Art
Cellular cores, commonly known as honeycomb stock, have been developed over recent years to supply the need for an inexpensive construction element having a high strength-to-weight ratio. These cellular cores are typically sandwiched between thin panels of sheet metal, or the like, to provide building components such as walls, partitions, doors, container panels, pallets and the like. These cellular cores are formed typically of sheet material such as paper, sheet metal, foil, and plastic.
The expanded cellular core preferably has the general shape and appearance of a honeycomb structure and therefore is commonly referred to as honeycomb. The unexpanded honeycomb core stock is fabricated by applying parallel but non-registering narrow stripes of adhesive to adjacent superimposed webs. When the adhesive is set, the webs of the honeycomb stock are expanded to form the cellular structure. Facing webs or backing sheets may be adhered on opposite sides of the expanded core structure which produces a low density structural element having great strength and resistance to loads applied normal to the facing webs.
According to the construction and operation of continuous honeycomb machines, unexpanded honeycomb stock is produced by continuously feeding a plurality of webs from a corresponding number of supply rolls which are journaled in bearings for free rotation about horizontal axes in response to a pulling force. During the continuous feeding, spaced parallel, longitudinal lines of adhesive are applied to opposite sides of one of the webs in non-registering relationship to one another. The continuous feed of both webs from supply rods is carried out by constant feed drive rolls which engage and continuously pull the webs from the supply rolls through the machine. Continuously driven feed rolls are provided to move the webs vertically downward in mutually superimposed and laminated condition toward a cutting zone, and a reciprocating cutter is provided to cut successive strips of the laminated webs of desired thickness. The cut strips are continuously packed into a packing throat and are laminated together to make a continuous length of unexpanded honeycomb material. In the vertical space between the cutter and the constantly driven feed rolls there is a take-up mechanism for accumulating excess web material which is delivered during the time that the reciprocating cutter is cutting.
The foregoing continuous feed arrangement and variations of it are commonly used for producing continuous honeycomb core. However, the efficiency and success of such conventional honeycomb machines which utilize a continuous web movement have been limited by certain technical problems associated with coordinating the continuous movement of a plurality of webs at a constant feed rate to an intermittently operating knife cutter. The construction of the constant drive apparatus is based upon the assumption that the paper conveyed by the constant drive apparatus is relatively inelastic and has substantially uniform properties along it length. However, in practice, a web of paper of the type typically used to make honeycomb stock has certain elastic properties which vary with temperature and humidity which allow it to stretch slightly under tension, as the ambient humidity and temperature varies. Additionally, variations of the winding tension applied to the webs as they are wound on their cores can cause variations in the relative weight of two supply rolls having the same diameter, thereby presenting unequal inertia loads to the constant drive apparatus.
Variations in the advancement of one web relative to the other may cause non-symmetrical cell formation which can lead to a quality control rejection of the core stock. Thus the web movement must be constantly observed by a trained operator to detect such variations and take corrective steps by adjusting the continuous drive apparatus from time-to-time as necessary. Because of the subtle nature of the variations of relative web movement and because of the nonlinear dynamic effects encountered in adjusting the feed of one web relative to the other, the operation of such a machine necessarily results in part from subjective determinations made by the operator and depends upon his skill and ability to make the necessary adjustment to the constant speed drive mechanism. Thus the quality of the core stock production in such a machine is directly dependent upon the experience level and skill of the operator.
The quality of the core stock is further limited by the slight inaccuracies in the driven rolls and the slight differentials in their surface speeds. It has been found that if more than a single pair of positive drive rolls are used, then there must be the utmost accuracy in synchronizing the surface speeds of such pairs of rolls with the result being to greatly increase the cost of manufacture of the machine. Thus the driver rolls must be engineered with micrometric accuracy for faithful service. It will be appreciated that such inaccuracies will increase as the moving parts are subjected to wear and age, and further that the effects of such inaccuracies are magnified as the operating speed is increased.
An additional problem relating to the operation of continuous honeycomb machines is that each time the thickness of the honeycomb stock is changed, the timing gears must also be changed. This requires that a set of timing gears be maintained corresponding to each desired core thickness. It will be appreciated that this requirement directly increases the capital investment involved, labor cost and down time of the machine.